1. Field of the Invention
The present general inventive concept relates to a robot control apparatus and a control method thereof, and more particularly, to a robot control apparatus and a control method thereof, which comprise a dual acceleration/deceleration processor to control an operation path of a robot.
2. Description of the Related Art
Generally, a robot control apparatus comprises an interpolator to keep an operation path of an industrial robot or the like, and to make the robot operate continuously between respective path modes.
Interpolation can be achieved by a circuit or a software module, which calculates disposition of respective joints provided in the robot at every control period so as to control the robot as a user wants, according to various path modes such as a linear path, a circular path, and a point-to-point path. Such an interpolator comprises an acceleration/deceleration filter, such as a low pass filter, to accelerate or decelerate a motor provided in a joint of the robot.
Such a conventional robot control apparatus is disclosed in Korean Patent Application No. 1997-80191 (U.S. Pat. No. 6,046,564), titled “PATH PLANNING APPARATUS AND METHOD FOR ROBOTS.” The conventional path planning apparatus for controlling a robot comprises an interpolator formed by a single low pass filter which receives a velocity profile Va calculated on a basis of a target positioning signal and performs a path interpolation to output a smoothed velocity profile Vb, and a servo controller which receives output of the interpolator and controls acceleration and deceleration of a servo motor. Thus, the conventional path planning apparatus for controlling the robot smoothes the operation of the servo motor through the interpolator formed by the single low pass filter, thereby decreasing damage in the robot.
However, in the conventional robot control apparatus, the interpolator employs the single acceleration/deceleration filter such as the low pass filter, so that a relatively large path error arises with respect to an input command path when the robot continuously operates along various path modes such as the linear path and the circular path.
FIG. 1 is a schematic representation of a set of operations of a conventional robot control apparatus, wherein the conventional robot control apparatus controls a robot to operate along a linear path LP and a circular path CP in sequence.
First, a linear velocity ΔX and a circumferential angular velocity Δψ are calculated by detecting a positioning signal from an input linear path LP and an input circular path CP. In the case of the linear path LP, the linear velocity ΔX can be used as an input value of an acceleration/deceleration filter 120. In the case of the circular path CP, the circumferential angular velocity Δψ can be used as the input value of the acceleration/deceleration filter 120. However, the linear velocity ΔX and the circumferential angular velocity Δψ are different in a dimension, so the linear velocity ΔX and the circumferential angular velocity Δψ are transformed into joint velocities (Δθ, Δθ′) through an inverse kinematics process before being inputted to the acceleration/deceleration filter 120 so as to prevent the input values that are different in dimension from interacting with each other in the acceleration/deceleration filter 120. Thus, the transformed joint velocities (Δθ, Δθ′) are used as the input values of the acceleration/deceleration filter 120, in sequence.
As described above, the conventional robot control apparatus comprises the single acceleration/deceleration filter 120, so the inverse kinematics process (refer to equation 1) should be performed prior to the acceleration/deceleration filter 120 in the case of a continuous operation between the different path modes. At this time, the linear velocity ΔX is nonlinearly related to the joint velocity Δθ so a relatively large path error arises during an acceleration/deceleration process. For example, the joint velocity Δθ obtained by the inverse kinematics process (refer to equation 1) is accelerated/decelerated by the acceleration/deceleration filter 120, and then a forward kinematics process (refer to equation 2) is used to check whether the accelerated/decelerated joint velocity Δθ is equal to the linear velocity ΔX. As a result of the check, a relatively large path error arises with respect to the input command path.Δθ=J−1·ΔX  (equation 1)ΔX=J(θ)·Δθ  (equation 2)                Where J(θ) is a Jacobian matrix.        
Thus, the conventional robot control apparatus is in need of an ability to operate the robot without a relatively large path error due to the single acceleration/deceleration filter with respect to an actual path.